This application claims priority of Taiwanese application. no. 90219607, filed on Nov. 14, 2001.
1. Field of the Invention
The invention relates to a vehicle security system, more particularly to one using alternating current signal transmission through a power supply line.
2. Description of the Related Art
Most vehicles are currently equipped with a vehicle security system in order to guard against vehicle theft. FIG. 1 illustrates a vehicle 2 equipped with a conventional vehicle security system 1. The conventional vehicle security system 1 comprises a host device 10 that controls all anti-theft operations, a detector circuit cluster 11 that detects different conditions of vehicle theft, and an alarm circuit cluster 12.
The detector circuit cluster 11 is connected to the host device 10 and is adapted to detect a current status of different components of the vehicle 2 for detecting signs of vehicle theft. The detector circuit cluster 11 includes an engine hood detector circuit 111 adapted to detect unauthorized opening of an engine hood 21 of the vehicle 2, a trunk hood detector circuit 112 adapted to detect unauthorized opening of a trunk hood 22 of the vehicle 2, a hand brake detector circuit 113 adapted to detect unauthorized movement of a hand brake 231 of the vehicle 2, door detector circuits 114 adapted to detect unauthorized opening of doors 24 of the vehicle 2, and a lock-pick detector circuit 115 adapted to detect insertion of a lock-pick into an ignition keyhole 25 of the vehicle 2. The conventional detector circuits 111-115 included in the detector circuit cluster 11 are in the form of switches that open and close in accordance with the current status of the respective component of the vehicle 2. Because each detector circuit 111-115 is connected to a voltage source, the host device 10 can determine the presence of unauthorized operation of the vehicle 2 by monitoring the voltage signals from the detector circuits 111-115.
The alarm circuit cluster 12 is connected to and controlled by the host device 10 to generate an alarm output in the event that unauthorized operation of the vehicle 2 was detected in accordance with the voltage signals from the detector circuit cluster 11. In general, the alarm output may be a visual output or an audible output. Since the vehicle 2 is equipped with a horn 26, exterior lighting 27 and interior lighting 28, the alarm circuit cluster 12 includes actuators connected to and enabled by the host device 10 to activate the horn 26, the exterior lighting 27 and interior lighting 28. Therefore, when the host device 10 detects unauthorized operation of the vehicle 2 in accordance with the voltage signals from the detector circuits 111-115, it will enable the alarm circuit cluster 12 so as to activate the horn 26, the exterior lighting 27 and the interior lighting 28, thereby deterring theft.
However, when mounting the conventional vehicle security system 1 on the vehicle 2, the detector circuits 111-115 and the alarm circuit cluster 12 require dedicated connecting lines for connection to the host device 10. In other words, a large amount of connecting lines are required to mount the conventional vehicle security system 1 on the vehicle 2. The mounting process is tedious, and the layout of the dedicated connecting lines is complicated. Furthermore, in the case that the vehicle security system 1 is not an original component of the vehicle 2, the mounting process will require rewiring of the vehicle circuitry, thereby further increasing the difficulty in mounting the conventional vehicle security system 1.
It is noted that the difficulty in mounting the conventional vehicle security system 1 will be greatly reduced if the existing vehicle circuitry can be used for signal transmission among the host device 10, the detector circuit cluster 11 and the alarm circuit cluster 12. Most components of the vehicle 2 require electric power for operation and are thus connected to the battery 29 via a respective power supply line. However, these power supply lines are used solely for dc power distribution. Even if the existing power supply lines are used to connect the host device 10 to the detector circuit cluster 11 in the conventional vehicle security system 1, the host device 10 will be unable to distinguish the voltage signals from the detector circuits 111-115 such that the host device 10 will be unable to detect unauthorized operation of the vehicle 2.
Therefore, the object of the present invention is to provide a vehicle security system that uses alternating current signal transmission through a power supply line to simplify the vehicle circuitry and to facilitate the mounting process.
Accordingly, the vehicle security system of this invention is adapted for use in a vehicle having a power supply and a power supply line connected to the power supply. The vehicle security system comprises a detector circuit cluster, an alarm circuit cluster and a host device.
The detector circuit cluster includes a plurality of detector circuits adapted to detect a current state of a respective component of the vehicle and adapted to be connected to the power supply line. Each of the detector circuits is capable of receiving a status request signal unique thereto via the power supply line, and transmitting a status response signal unique thereto and corresponding to the detected state of the respective component via the power supply line in response to the status request signal.
The alarm circuit cluster is adapted to be connected to the power supply line and is capable of receiving an alarm enable signal distinct from the status request and status response signals via the power supply line. The alarm circuit cluster is enabled so as to generate an alarm output upon receipt of the alarm enable signal.
The host device is adapted to be connected to the power supply line, and is capable of transmitting the status request signals for the detector circuits in sequence via the power supply line, receiving the status response signals from the detector circuits via the power supply line, and selectively transmitting the alarm enable signal to the alarm circuit cluster via the power supply line in accordance with the status response signals from the detector circuits.
Each of the status request signals, the status response signals and the alarm enable signal is in the form of an alternating current signal.
Because the status request signals, the status response signals and the alarm enable signal are alternating current signals that are distinct from the power signal normally distributed through the power supply line, signal transmission among the detector circuit cluster, the alarm circuit cluster and the host device can be carried out via the power supply line to simplify the vehicle circuitry and to facilitate installation of the vehicle security system of this invention.